import java.util.ArrayList;

/**
 * 输入一个矩阵，按照从外向里以顺时针的顺序依次打印出每一个数字，
 * 例如，如果输入如下4 X 4矩阵： 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
 * 则依次打印出数字1,2,3,4,8,12,16,15,14,13,9,5,6,7,11,10.
 */
public class Solution29 {
    public ArrayList<Integer> printMatrix(int[][] matrix) {
        if (matrix == null || matrix.length == 0 || matrix[0].length == 0) {
            return null;
        }
        ArrayList<Integer> result = new ArrayList<>();

        if (matrix.length == 1 && matrix[0].length == 1) {
            result.add(matrix[0][0]);
            return result;
        }

        int left = 0;
        int top = 0;
        int bottom = matrix.length - 1;
        int right = matrix[0].length - 1;

        while (left <= right && top <= bottom) {
            // 向右
            for (int i = left; i <= right; i++) {
                result.add(matrix[top][i]);
            }
            // 向下
            for (int i = top + 1; i <= bottom; i++) {
                result.add(matrix[i][right]);
            }
            // 向左
            for (int i = right - 1; i >= left && top < bottom; i--) {
                result.add(matrix[bottom][i]);
            }
            // 向上
            for (int i = bottom - 1; i > top && left < right; i--) {
                result.add(matrix[i][left]);
            }
            top++;
            right--;
            bottom--;
            left++;
        }

        return result;
    }
}
